Solvent recovery in dewaxing operations



INVENTOR /r ATrORNEY H. L.. DUFFY SOIJVENT RECOVERY IN DEWAXING`OPERATIONS Filed Nov. 14, 1955 S au SWTES PATENT "OFFICE 'I SOLVENTRECOVERY IN DEWAXIN DPERATIONS Herbert Lewis Duffy, Sumner, Ill.,assignor to Indian' Refining Company, Lawrenceville, Ill.,

a corporation of Maine Application November 14, 1935, *Serial No. 49,704

11 Claims.

This invention relates to the solvent dewaxing of mineral oil, and moreparticularly to the recovery of solvent from slack wax separated in sucha solvent dewaxing process. Y

In the solvent dewaxing oi mineralen as customarily practiced,`the oilto be dewaxed is mixed with a solvent, the oil-solvent mix chilled toprecipitate the-wax, and the precipitated wax sepa.- rated by iltration,centrifuging, or cold settling from the resultant dewaxed oil. Someofthe solvent employed in the process is retained in the separated slackwax, the bulk of the solvent being retained in the dewaxed oil. l Anywater present inthe system as ari-impurity freezes out and is separatedalong with the slack wax. The rei tained solvent is then generallyrecovered from lation for reuse in the process. i

The water presentin the slack .wax frequently causes diiiiculty in therecovery of solvent from both-the dewaxed oil and the slack wax bydistilthe slack wax, vparticularly where a solvent is em-, ployed whichis miscible or soluble in water. 'I'his the water will also be vaporizedand passed along` with the solvent vapors. L

When these vapors are condensed, they will separate into an upper layercontaining substan- 'tially'all the benzol and toluol together withacetone and enough water to saturate this top layer' and a lower layercontaining water and dissolved acetone. At condenser temperatures ofF.'to F., a solvent composed of 35% acetone, 52% benzol and 13% toluol,for example. willdissolve about 11/2% of water when saturated. `Incommercial operation, there is always enough'moisture present tosaturate the solvent and this 11/2 of dissolved water seriouslyinterferes with yields, rates of ltration and quality of yieldii thesolvent is reused without removing the water. It is dii'- ilcult toseparate the dissolved water from the top layer containing benzol,toluol and acetone so as to eect a substantially complete recovery ofthe solvent, which is desirable in commercial practice in order toreduce solvent loss and render the process commercially economical. Onthe other hand, ii the waterv is not separated from the system it will`gradually accumulate and dilute the' solvent and this destroys itseffectiveness as a dewaxing solvent.

It is an object of the present inventionto provide a method ofrecovering solvent from slack wax in a dewaxing process ofthis characterand employing a solvent which is miscible with water, in a simple andcommercially economical 'manner, while at the same timeeiectingasulistantially complete recovery o! the solvent.

It is a further object of the invention to' substantiallycompletelyremove water from the recovered solvent, and to do this in asimple and expeditious manner avoiding heat loss.

In the drawing, the single figure is a diagram- `10 matic view ofapparatus for carrying out the method of this invention.

In accordance with the presentinvention, the slack wax-solventmix-separated from the chilled solvent-oil mix is heated to a controlledtemperature at which the slack wax-solvent mix becomes thin enough topermit the separated water to settle out. This temperature issubstantially the temperature at which the precipitated wax becomesdissolved in the solvent. Until this temperature is reached, theprecipitated Wax makes the mixture so thick that the particles of waterwill not settle out although they are separated in the form of smallglobules distributed throughout the mix. The mixture is allowed to standat this V maintained temperature, whereupon -it settles into a lowerwater layer containing a'very small proportion of the solvent, and anupper4 wax-oil layer containing the major proportion of the solvent. Thetwo layers'are then separated as by decantation. The solventlsthen'recovered from the upper wax-oil layer by distillation. Any ismall proportion of retained solvent 'may be re' covered from the lowerwater layer by stripping the same with steam and fractio'nating thevapors to carry overhead substantially pure 'solvent uncontaminated withwater.' 'I'his is'found `feasible where only a small Aproportion of thesolvent is left in the water. The solvent recovered from the two layersmay be condensed' and combined. '40 The recovered -solvent is thenchilled to la low temperature approximating the dewaxing temperature tofreeze out any small amount of water remaining therein. The chilledsolvent, freed Iof water, is then preferably adxlnixed directly withchilled wax bearing mix passing to the lters or i other' wax `separatingmeans. Preferably, 'the recovered solvent from the distillation and con-:lensing-zone is passedin heatl exchanging relationship with the slackwan` from thewax lters or wax separating zone in order to heat theyslack wax andl at the same time cool the solvent.

Referring to the drawing, which illustrates ap paratus for carrying outa preferred embodiment oi the invention, chilled oil-wax bearing mix tov55.

' storage for recovery oi the bulk of the solventA which is retainedtherein. The slack wax is discharged from lter H through line I5 toreceiver i6..

By way of example, the present invention is defscribed in connection.with the acetone-benzol dewaxlng process, asillustrated in fthe patentto Gevers No. 11,802,942. In this process, the oil to be dewaxed ispreferably mixed with about three to four volumes of solvent comprisingabout acetone and 65% benzoL AOra solvent mixture, of acetone, benzolvand toluol may be em# ployed; 'The benzoland'toluol arenot miscible withwater-and little diiliculty is experienced in their recovery.7 However,the acetoneis miscible and soluble in water and is `representative of asolvent of the classembraced herein, in which difficulty is experiencedin recovering the solvent4 free from water.' Whilethe invention isparticularly described inconnection with the recovery of acetone andbenzol from slack wax.

it is lto be understood that it is not confined to this particularsolvent mixture, but is applicable more generally to solvents or solventmixtures which contain a. constituent or constituents miscible with orsoluble in water to a` certain extent at normal operating temperatures.For example, theinvention may be applied to other ketones -such asmethyl ethyl ketone, hexone or methyl isobutyl ketone, etc., and tomixtures thereof with benzol, toluol and the like. A

In accordance with the present invention, the slack wax is pumped fromreceiver I 6 by pump I8 through line I9 to heat exchanger 20, where'itis passed in heat exchanging relationship with hot recovered solventintroduced by line 2l. This serves to. heat the slack wax whileconcurrently cooling the recovered solvent. .The preliminarilyheated'slack wax then passes 'by line 22 to steam heater-23 where it isheated-to a controlled temperature at which the wax and retained oilhave a greater afllnity for the water soluble solvent, in

this case acetone, than has water which may be present therein. Theheated slack wax then pass- 1 proportion .ofthe water solubleconstituent.

es by line 2t into an intermediate portion of a settling drum 25. Herethe mix is4 allowed to stand and settle into an upper wax-oil layercontaining a major proportion of the solvent and.

a lower `water layer containing a very small In the case oithelacetone-benzol dewaxing process,

it is found that by. heating .the slack wax to a temperatureof the orderof 88 F., andv allowingthev slack wax to stand at this temperature, thelower water layer which separates out contains' about 25% of acetone,the bulk of the acetone and substantially all of-the benzol being'retained inthe upper Wax-oil layer.. The lower water layermay vbewithdrawn continuously or periodically through line 26 into receiver21fproi vided with vent 28.

The wax-oil.layer, separated from -the bulk of .fthe vwater,overflowsfrom drum25 and. passes byline 3B' through heat exchanger coil 3l invapor heat exchanger 3'2, and then by 'line33'through exhaust steamheater 34, and finally by line 35 -lnto slack waxzfiash drum .36. Slackwax from the bottom of drurnf36 is withdrawn by pump 3l abscess andpassed by line 38 through 'heating coil 39 positioned within a suitablefurnace, and then returned by line 40 to the upper vapor portion of drum36. In this manner, most of the solvent is flashed off from the'wax. Aportion of the stream passing through line 38 is diverted through line42 to a steam stripping zone (not shown), where remaining solvent isremoved from the slack wax. The slack Wax is then passed to a receiverfor storage or further treatment.- As -this portion of the apparatus isconventional and forms no part of the present invention, further'description and illustration thereof is thought unnecessary. Solvent'vapors flashed off in drum 36 pass by vapor line 63 through heatexchanger 32, then into water cooled condenser 44 where they arecondensed, and flow by line 45 into solvent receiver t6 equipped withvent 41.

The lower water layer containing a small proportion ofsolvent, such asacetone, is withdrawn from receiver 2l by pump 50 and forced throughline 5| through steam heater 52 and then introduced by line 53 into anintermediate portion of stripping column 54. The stripping column 5lsurmounts an evaporator chamber 55 into which steam is introduced byline 56. 'I'he steam passing acetone serves to. strip the acetonetherefrom substantially completely, and the stripped vapors of acetoneand steam pass upwardly through the column 54 countercurrent to adescending stream of reflux introduced, by line 5T. This serves tocondense most of the steam, so that mainly acetone passes overhead towater cooled condenser 58 where it is condensed, and then ows intoreilux drum 59. A portion of the condensed liquid 65 where it isrefrigerated to a low temperature approximating the dewaxingtemperature. For example, it may be chilled to about -10 to -20 F. 'I'hechilled solvent then passes by linev66 to a receiver 6 1, where anymoisture remaining in the solvent and which was frozen out in chiller 65is separated. The chilled solvent Vfreed of moisture then passesbyline58 lntoline l0 where it meets the chilled oil-wax mix, and these arethoroughly mixed by passing through a suitable turbulent flow mixer 69before'belng introduced into filter H or the surge drum `I2. In thismanner, the chilled solvent is returned to the system at a point wherethe temperature of the system approximates that of the solvent, avoidingheat or refrigeration loss.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof and only'such limitations should be imposed as areindicated inv the appended claims.

I claim:

l. In the dewaxing of mineral oil, wherein the oil to be dewaxed ismixed with a solvent comprising acetone, the mixture chilled toprecipitate wax, and the resultant slack wax with retained oil andsolvent is separated from the oil; the method of recovering retainedsolvent from "the lseparated slack wax, which comprises heatupwardlythrough the heated water containing ing the slackwax to a controlledtemperature at which the wax becomes dissolved in the re tained solvent,allowing the mixture to` stand at the controlled temperature to settleinto a bottom Water layer containing a -minor proportion of dissolvedacetone, and an upper Wax-oil layer containing the major proportion ofthe solvent, separating the layers, and then recovering the solvent fromthe separated wax-oil layer.

2. The method of claim 1, in which the slack wax is heated to atemperature of the order of 3.- The method of claim 1, in which theseparated water layer is subjected to stripping with steam and theresultantv vapors fractionated to separate retained actone from thewater. and

the separated acetone returned to the system.

4. The method of claim 1 in which the slack wax is heatedl by heatinterchange with recovered solvent.

5. The method of claim 1 in'which the solvent is recovered from theseparated Wax-oil layer by distillation, retained solvent in the bottomwater -layer is recovered by steam stripping, the recovered solventscombined andtchilled to freeze out any remaining water therein, and thechilled solvent freed of water returned to the system.

6. The method of claim 1in which the solvent is recovered from theseparated wax-oil layerby distillation, recovered solvent is returned inheat exchanging relationship with slack wax to heat the slack wax andcool the recovered solvent, and the cooled solvent is then chilledtofreeze out any remaining water therein prior to return to the system.

7. Themethod of 4claim 1 in which the solvent is recovered from' theseparated wax-oil layer by distillation, the resultant solvent vaporscondensed, the condensed solvent chilled to freeze out any remainingwater therein, and the chilled recovered solvent introduced into andmixed with the chilled 4oil-solvent mix passing to the wax separationstep.

8. In the dewaxing of mineral oil, wherein oil to be dewaxed is mixedwith a solvent comprising a constituent which is soluble in water atnormal temperatures but which is primarily retained in wax and oil asopposed to water at elevated temperatures, the oil-solvent mix chilledto precipitate wax,a`nd the resultant slack wax with retained oil andsolvent is separated from the oil; the method oi recoveringretainedsolvent from the separated slack wax, which comprises heat ing the slackwax to a. controlled temperature at' which the wax becomes dissolved inthe retained solvent, allowing the mixture to stand atthe controlledtemperature to settle into a bottom water layer containing a minorproportion of the solvent4 constituent dissolved therein, and an upperwax-oil layer containing the major proportion of the solvent, separatingthe layers, and then recovering the solvent from the separated wax-oillayer. y

9. The method of claim 8, in which the separated 'water layer issubjected to stripping with steam and the'vapors fractionated toseparate retained solvent constituent from the water, and

, the separated solvent constituent returned to the system. l

10. The method of claim 8 in which the slack 'wax is heated `by heatinterchange with recovered solvent.

11. `The' method of claim 8 in which solvent is recovered from theseparated' waxoil layer vby distillation', the solvent vapors condensed,the

' condensed 'solvent chilled to freeze out any remaining watenand thechilled recovered solvent returned to the system.

HERBERT LEWIS DUFFY.

